To be certain, you should:
* Consult your owner's manual: This is the best resource for the precise location on your specific model.
* Check online repair manuals: Sites like Chilton or Haynes offer detailed diagrams and information for your year and model. Search for "1997 Chevrolet Astro fuel vapor canister location."
* Look for a charcoal-like canister with hoses connected: The canister is usually cylindrical and black or dark gray. It will have hoses connected to it, leading to the fuel system and potentially the intake.
It's best to visually inspect your Astro van under the vehicle after consulting those resources. Be careful when inspecting underneath the vehicle, and use jack stands for safety if you plan to get underneath.